For safety reasons, it is required that the doors of electrical appliances and in particular of domestic electrical appliances, such as e.g. washing machines, dishwashers and tumble driers, may not be opened while an appliance is in operation. This is to prevent a user from being injured by rotating components of an electrical appliance, such as e.g. a drum of a washing machine or rotating arms of a dishwasher, if he attempts to open the appliance while in operation. It is also to prevent water or hot air from escaping because of an unintentional, even only partial opening of an appliance door.
For said purpose, locking or blocking apparatuses are usually used which, upon or after starting of an electrical appliance with a closed appliance door, lock a door lock or a door interlock for the appliance door in such a way that during the continuous operation of the electrical appliance the door of the latter may not be opened. In an operating state of the electrical appliance, in which it is intended that the appliance door may be opened, the door lock or the door interlock is released for opening. Such an operating state generally exists at the end of the actual operation of the electrical appliance (e.g. wash or drying programs). Such operating states may however also exist during the actual operation of the electrical appliance when opening of the appliance door may be effected without risk.
While the unlocking function of locking or blocking apparatuses may be provided during normal operation, unlocking of a door lock or a door interlock by means of such apparatuses is normally no longer possible when the electrical appliance, in a departure from desired operating states, is in an abnormal operating state. This is the case, for example, when there is a failure of the power supply for the electrical appliance, or the electrical appliance is not connected to an electrical power supply. Locking or blocking apparatuses, which prevent an undesirable opening of the appliance door of an electrical appliance during normal operation, are operated generally by means of electrical energy. Thus, a failure or absence of an electrical energy supply leads to an inability to open an appliance door which is secured or locked during normal operation by such an apparatus.
Prior Art
From DE 196 01 228 C2 it is known to lock the door of a washing machine or dishwasher during normal operation by means of an apparatus, which comprises a bolt nab or a door catch and a locking body. The locking body in an open position releases the bolt nab or the door catch for opening of the door, whereas in a closed position it prevents the bolt nab or the door catch from opening the door. To bring the locking body into the open position and the closed position a bistable element is used, which is preloadable into two positions by means of a force-generating element. In a first position the bistable element prevents a movement of the locking body out of its closed position into its open position. In a second position, on the other hand, the bistable element enables a movement of the locking body out of its closed position into its open position. The bistable element therefore provides the previously described locking and release function during normal operation of a washing machine or dishwasher.
The bistable element is moved into its first and its second position by means of two independent magnets, wherein for crossovers between the positions a snap point has to be overcome, which is provided by a spring used as the force-generating element. Furthermore, use is made there of a safety bolt, which by means of the bistable element arrests the locking body in its closed position and, for release of the locking body, is brought by the bistable element out of engagement with the locking body.
In order in an abnormal operating state of the washing machine or dishwasher, which is referred to as an emergency situation, to bring the locking apparatus described there into the open position for opening of the door, an emergency unlocking lever is provided. The emergency unlocking lever to be operated by a user moves the safety bolt in such a way that the latter is brought out of engagement with the locking body. Operation of the emergency unlocking lever may be effected e.g. by means of a cable pull or Bowden wire, which is normally run to a side wall or the base of the washing machine or dishwasher.
Said emergency unlocking device however also allows the appliance door to be openable during normal operation of the washing machine or dishwasher because a user may independently, through operation of the emergency unlocking lever, deactivate the safety measures provided by the locking apparatus against undesirable opening of the appliance door. A further drawback is that in an abnormal operating state of the washing machine or dishwasher the emergency unlocking is to be effected manually by a user. This is sometimes a complicated procedure because the cables used to operate the emergency unlocking lever are disposed at points which are difficult to access. It is moreover necessary for the user to be informed about how emergency unlocking is to be effected.
To eliminate the drawbacks of an emergency unlocking effected by a user, according to EP 965 677 A1 use is made of a locking apparatus, which comprises a blocking element, which is movable by means of a thermoelement, and a release element, which is movable by means of an electromagnet. During normal operation of a domestic appliance, in which said locking apparatus is used, the thermoelement is heated by supplying energy in such a way that it moves the blocking element into a blocking position, which locks a bolt nab or a door catch of an appliance door to prevent undesirable opening. If during normal operation of the domestic appliance an opening of the appliance door is to be permitted, the release element is moved by means of the electrically activated electromagnet in such a way that it brings the blocking element out of the blocking position into a release position. In the release position there is no working connection between the blocking element and the bolt nab or the door catch. During normal operation the blocking element is held in its blocking position by the thermoelement, which for suitable heating and the resultant positioning is supplied with electrical energy.
When there is no electrical energy available for operating the domestic appliance and hence for operating said locking apparatus, the thermoelement is also no longer heated. The thermoelement accordingly cools down and moves into its original position, with the result that the blocking element is no longer held in its blocking position but moves into its release position. In said manner, an emergency unlocking is provided, for which no measures are to be taken by a user.
The drawback here is that the thermoelement is used to bring the blocking element into the blocking position and hold it in the blocking position. Because of the time it takes to heat the thermoelement to such an extent that the blocking element is brought into the blocking position, said locking apparatus does not inevitably lock the appliance door at the same time as the domestic appliance is set in operation. Especially in domestic appliances, in which rotating components are used, this may constitute a danger. Because of the time delay before locking, a user may immediately after start-up of the domestic appliance open its door again and be injured by coasting rotating components. What is more, the thermoelement does not guarantee that the blocking element is held reliably in its blocking position because, for said purpose, it is necessary for the thermoelement to be heated by supplying energy to it during normal operation of the domestic appliance. Thus, for example, failure of the thermoelement or of its electrical supply may lead to the appliance door being releasable and hence openable during operation of the domestic appliance.
A further drawback of said locking apparatus is that the locking function and the release function are provided by separately constructed devices, namely the blocking element and the release element. This is constructionally complex and may lead to the blocking element and the release element cooperating in an undesirable manner, more precisely, being moved against one another. Furthermore, the release element has to overcome the forces, which are summoned up by the thermoelement for holding the blocking element in its blocking position, in order to bring the blocking element into the release position. This leads to a higher energy demand for release of the appliance door and may lead, e.g. as a result of wear phenomena, to damage of the thermoelement.